The emergining use of low-rate coding and digital transmission in mobile satellite communications and the increasing use of facsimile services have identified the desirability for visual service transparency over the same very narrow-band circuits. The economic viability of such a service, however, rests on the capability of introducing further image message compression, either in real-time or off-line (in store and forward). In addition to the economic side however, long document transmission times negatively impact the customer perceived quality of service in that, over narrow-band circuits, several minutes might be required for the transmission of documents that would normally need only seconds when transmitted through the public switch telephone network. In order to achieve these objectives, some form of image compression over and above what is provided by traditional Group 3 facsimile is needed.
Generally, this compression can only be achieved at the expense of message quality. However, since these types of services are not typically offered over the public switched telephone network, considerable leeway is available for techniques that primarily focus on the retention of a high degree of message intelligibility over a narrower range of input documents, rather than attempting to achieve the broader scope of preserving quality over a very wide range of possible images.
The following are examples of facsimile compression and decompression systems.
U.S. Pat. No. 4,796,092 to Ogata discloses an image processing system for facsimile devices which electrically transmit image data. According to this system, an image signal is coded using run length coding, and then the coded image signal is stored in an image memory. The coded signal is then read out from the image memory and processed a plurality of times.
U.S. Pat. No. 4,794,461 to Roberts et al discloses a compression system for facsimile image data. The system includes block coding one or more vertical mode codes produced by standard CCITT facsimile processes.
U.S. Pat. No. 4,134,133 to Teramura et al discloses a system for interline-coding a facsimile signal. The system includes alternately dividing information of scanning lines of an input facsimile signal.
U.S. Pat. No. 4,558,371 to Rallapalli et al discloses a system for two-dimensionally coding digital facsimile signals. The system includes coding the positions of the color change picture elements in a coding line of digitized picture data with respect to the position of change picture elements in a reference line of digitized picture data.
U.S. Pat. No. 4,115,815 to Nakagome et al discloses a facsimile signal coding method in which information change picture elements are classified into two kinds of change points according to the information change directions.
U.S. Pat. No. 4,040,093 to Nakagome et al discloses a system for coding information change picture elements in a facsimile signal in which the information change picture elements of consecutive scan lines are examined in order to minimize the number of bits of each code word.
U.S. Pat. No. 4,360,840 to Wolfrum et al discloses a real time data compression scheme for facsimile transmission systems. The scheme includes compressing a graphic image using an entropy preserving algorithm which allows for real time reduction of pel-to-pel data.
U.S. Pat. No. 3,991,267 to Beaudette discloses a method for producing compressed digital data in which binary line scan functions are translated into equivalent binary codes of reduced redundancy and length.
U.S. Pat. No. 3,909,514 to Tanaka et al discloses a facsimile communication system in which code signals are generated which indicate a sequence of background area. These code signals are subsequently used to regenerate the original image.
U.S. Pat. No. 4,117,517 to Shintani et al discloses a data compression system for binary facsimile signals. In this system, the binary bit pattern of each scan line is compared with that of the adjacent scan line just above it, and any bit pattern variations are identified as belonging to one of several predetermined modes which are translated into codes. These codes are transmitted instead of the image in order to provide image compression. Those variations which do not belong to any of the predetermined modes are transmitted uncoded.
U.S. Pat. No. 4,121,258 discloses a method for coding facsimile signals in which addresses of information change elements, each having information different from the immediately preceding picture element on the same scanning line of a facsimile signal, are encoded.
U.S. Pat. No. 4,212,035 to Nakagome et al discloses a facsimile signal coding system in which a facsimile signal is divided into a plurality of scanning line groups. A central one of the scanning lines of each group is encoded by a coding method which does not refer to information of a scanning line adjacent to the central scanning line.
U.S. Pat. No. 4,893,187 to Tsujimoto et al discloses an image processing apparatus which includes an exclusive OR processing circuit for carrying out an exclusive OR operation on pairs of read image lines.
U.S. Pat. No. 4,163,260 to Hisao et al discloses a system for compressing band width of an image by logically combining each picture element on at least two scan lines to form two sections, and run length-coding one of the two sections.
U.S. Patent to Yamazaki et al discloses a coding method for two-dimensional coding of a two-level facsimile signal.
U.S. Pat. No. 4,212,036 to Nakagome et al discloses a method for coding addresses of information change picture elements.
U.S. Pat. No. 4,245,247 to Fike et al discloses a system for recording facsimile on a video disc.